The present invention relates to pearlescent pigments based on substrates coated with one or more layers of nitrides or oxynitrides, to methods for the production of such pigments and to their use in plastics, paints, coatings, powder coatings, inks, printing inks, glasses, ceramic products, agriculture foils, for lasermarking of papers and plastics and in cosmetic formulations.
The pearlescent pigments that are used and prepared according to this invention are at least partially transparent pigments with an angle-dependent optical effect.
Absorption pigments without any substrates based on nitrides or oxynitrides are well known. A good overview over these substances can be found in Marchand et al. xe2x80x9cNitrides and Oxynitrides: Preparation, Crystal Chemistry and Properties,xe2x80x9d Journal of the European Ceramic Society, 8 (1991), p 197-213. It is characteristic for these pigments that through the variation of the metal oxides or mixed oxides and/or a variation in the N/O ratio a wide range of the color spectrum can be covered. These pigments are synthesized by simply mixing the metal oxides together with a mineralizer and subsequently heating this mixture under an ammonia gas atmosphere.
Titanium nitride coated substrates used as conductive pigments and produced in a fluidized bed reactor are disclosed in EP-A 0 401 141. Here, substrate particles were to be made conductive by a coating with titanium nitride. To achieve this, mica powder is coated via CVD in a fluidized bed apparatus at a constant temperature. As reactants a titanium halide and ammonia, mixed with an inert gas such as argon, are used.
Titanium oxynitride coated SiO2 platelets are disclosed in WO2000/17277. In this application TiO2/SiO2-flakes are reduced with a metal under a non-reductive atmosphere at high temperatures using a metal halide as accelerator. The resulting product consists of titanium oxynitride-coated SiO2 platelets and titanium suboxide coated SiO2 platelets. Titanium nitride and oxynitride layers made according to this technology have turned out to be non-continuous and consequently showing brownish to olive colors. These rather unattractive colors were already described in the examples of WO 2000/17277.
It was therefore an object of the present invention to provide pigments with a great variety of different masstones which combine an attractive angle dependant interference phenomenon with the absorption color, therewith extending the range of pearlescent pigments based on substrates coated with nitrides/oxynitrides. Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The present invention now provides new kinds of pigments which are based on nitride, respectively, oxynitride layers on substrates. These pigments are based on substrates coated with a selectively absorbing layer.
Surprisingly, a pearlescent pigment has now been found, which is based on substrates coated with one or more layers, characterized in that at least one layer is selectively light absorbing and consists of a nitride and/or oxynitride with the proviso that layers of titanium nitride or titanium oxynitride are excluded.
Preferably the synthesis of the new pigments is divided into two steps. The first step is the synthesis of a precursor and the second a conversion process carried out in a furnace. The new pigments can be produced in conventional static ovens, belt kilns or rotary kilns. However, a better product with less agglomerates and faster reaction rates is obtained in fluidized bed reactors.
The precursor is preferably produced in an aqueous precipitation process such as described for example in U.S. Pat. Nos. 3,087,828, 3,087,829, DE-A 19 59 998, DE-A 20 09 566, DE-A 22 14 545, DE-A 22 44 298, DE-A 23 13 331, DE-A 25 22 572, DE-A 31 37 808, DE-A 31 37 809, DE-A 31 51 343, DE-A 31 51 354, DE-A 31 51 355, DE-A 32 11 602, DE-A 32 35 107, WO 93/08237 and EP-A 0 763 573. Halide, carbonate, oxalate, chloride, oxychloride or alcoholate solutions are used to precipitate oxides, respectively, mixed oxides onto substrates. The reaction parameters such as temperature, pH, agitation velocity and reactor geometry are optimized to yield a flat continuous layer of insoluble oxides and/or hydroxides on the substrates. The mixed oxides are coprecipitated onto the substrates following an analogous process. For example, solutions of the different metal salts are mixed and then slowly added in the reactor to coat the substrate.
A wide range of precursors can also be synthesized using dopant ions, such as silicon, vanadium, chromium, aluminum, cerium, neodymium, praseodymium, sulfur, selenium, cobalt, nickel, zinc and phosphate ions, coprecipitated into the oxide respectively hydroxide layers. The dopants can be used to create color effects (like rare earth, vanadium, or cobalt ions) as well as for the control of grain growth (like SiO2 or aluminum oxide) during the subsequent reaction with the reaction gas, such as ammonia. Advantageously this process does not need mineralizers or other reactive gases.
In the second step the precursors obtained in the above first step are converted into nitrides/oxynitrides. The precursors to be converted are calcined, for example, in a conventional static oven, belt kiln or rotary kiln. However, a better product with less agglomerates and faster reaction rates is obtained in a fluidized bed reactor. This process can be performed batchwise or continuously. A suitable mixture of gases consists of at least one inert and one reaction gas. Examples of useful reaction gases are N2, or N2/H2, but preferably ammonia. Further examples of converting to nitrides are shown in U.S. Pat. No. 5,246,493 and the above-cited Marchand article. Suitable inert gases are Ar, H2/CO/N2, N2 (at lower reaction temperatures). The gas composition may vary from  greater than 0 to 100 vol.-%, preferably from 20 to 80 vol.-% of reaction gas in inert gas.
The temperature is maintained during calcinations, for example, at a fluidized bed temperature at 700 to 1250xc2x0 C., preferably 800xc2x0 C. to 1100xc2x0 C. The conversion from oxides/mixed oxides to nitrides/oxynitrides is carried out depending on the different parameters, such as gas flow rates, reaction time or temperature profiles. The longer the reaction time the higher the nitride-to-oxynitride ratio. Consequently the reaction time determines the obtained structure of the compound. The color and the color strength of compounds is associated to a specific structure; thus, it is preferred that the reaction time is well controlled. In addition, for the same reason, temperature control is desirable.
In order to maintain the almost ideal conditions prevalent in a homogeneous fluidized bed in comitercurrent/cocurrent contacting special devices may be used. Instabilities like formation of channels or of bubbles in the bed are instantly destroyed by vibrations or agitating facilities.
If the reaction with the reaction gas, preferably ammonia, is not carried out to full completeness, mixtures of phases can be obtained including gradient of phase concentration through the layer thickness. These incompletely reacted products can be advantageous with respect to a desired color shade.
Suitable substrates which can be used in the present invention as base material, include, for example, spherical or platelet-shaped substrates, especially preferred are natural micaceous iron oxide (for example as in WO 99/48634), synthetic and doped micaceous iron oxide (for example as in EP-A 0 068 311), mica (muscovite, phlogopite, fluorophlogopite, synthetic fluorophlogopite, talc, kaolin), basic lead carbonate, flaky barium sulfate, SiO2, Al2O3, TiO2, glass, ZnO, ZrO2, SnO2, BiOCl, chromium oxide, BN, MgO flakes, Si3N4, graphite, pearlescent pigments (including those which react under the fluidized bed conditions to nitrides, oxynitrides or by reduction to suboxides etc.) (for example EP-A 9 739 066, EP-A 0 948 571, WO 99/61529, EP-A 1 028 146, EP-A 0 763 573, U.S. Pat. No. 5,858,078, WO 98/53012, WO 97/43348, U.S. Pat. No. 6,165,260, DE-A 15 19 116, WO 97/46624, EP-A 0 509 352), pearlescent multilayer pigments (for example EP-A 0 948 572, EP-A 0 882 099, U.S. Pat. Nos. 5,958,125, 6,139,613), coated or uncoated SiO2 spheres (for example known from EP-A 0 803 550, EP-A 1 063 265, JP-A 11 322 324), EP-A 0 803 550, EP-A 1 063 265, JP-A 11 322 324), micro bubbles (U.S. Pat. No. 4,985,380). Particularly preferred are mica, SiO2 flakes, Al2O3 flakes, TiO2 flakes, Fe2O3 flakes, BiOCl and glass flakes.
The layer(s) that is (are) precipitated onto the substrates and then converted result in the following nitrides and/or oxynitrides, for example:
in case of nitrides:
1) binary nitrides of the formula
-AxNy with A=Ta, Zr, Si, Al, V, Nb, Cr, Mn, W, Mo, Fe, Li, Mg, Ca, Sr, Zn, Ga, P particularly Ta3N5, Zr3N4, Si3N4, Fe3N, GaN, CrN
0 less than x, 0 less than y
2) ternary nitrides of the formula
AxByNz such as NaPN2, NaGe2N3, MgSiN2, BeSiN2, MgSiN2, MnSiN2, MgGeN2, MnGeN2, ZnGeN2, LiSi2N3, LiGe2N3, NaGe2N3, Mg2PN3, Mn2PN3, Zn2PN3, LaSi3N5, CrYN, CrScN, CrLaN,
0 less than x, 0 less than y, 0 less than z
Li2nxe2x88x923MnNnxe2x88x921 with the oxidation state n of the metal M ranging from 2 to 6, such as LiMgN, LiZnN, Li3AIN2, Li3GaN2, Li5SiN3, Li7VN4, Li7MnN4, Li9CrN5, Li2ZrN2, Li2CeN2, Ca2ZnN2,
in case of oxynitrides:
1) oxynitrides based on one metal
AxOyNz, with A=Ta, Al, Zr, Nb, Si, P, Hf, particularly Zr7O8N4, Zr2ON2, Zr7O11N2, Hf2ON2, Al3O3N, Ga1xe2x88x92x/3N1xe2x88x92xOx with 0 less than x less than 1
0 less than x, 0 less than y, 0 less than z
2) oxynitrides based on two metals
ABO2N, with A=Lanthanide, B=Si, particularly: LaSiO2N
ABO2N, with A=Ca, Sr or Ba B=Ta or Nb particularly: CaTaO2N, SrTaO2N, SrNbO2N, BaTaO2N, BaNbO2N
ABON2, with A=Lanthanide, B=Ta, Nb, particularly: LaTaON2 
ABON, with A=alkaline and B=Ge or Si particularly: NaGeON, KGeON, LiSiON, NaSiON
A2BO3N, with A=Ca, Sr, Ba and B=Ta, Nb
ABO3xe2x88x92xNx, with A=Li+, Na+, K+, Rb+, Cs+, Ba2+, Sr2+, Pb2+, Ln3+(=rare earth), Bi3+, Y3+ B=W6+Re6+Mo5+, Ta5+, Nb5+, Mo5+, W5+, Zr4+, Sn4+, Ge4+, Nb4+, Ta4+, Al3+, Ga3+, Ln3+ (=rare earth), Fe3+, Cr3+ and with x=1, 2 or 3 and the electronic charges a of A and b of B verify a+b=6+x; axe2x89xa7x and solid solutions of these compounds
ABO3N with A=K or Cs B=Os particularly: KOsO3N, RbOsO3N, CsOsO3N
A2BO3N with A=Sr or lanthanide B=Ta particularly: Sr2TaO3N
Li1+xGe2xe2x88x92xO3xN3xe2x88x923x 
(0 less than x less than 1)
LnWOxN3xe2x88x92x with Ln=La and Nd and 0,6 less than x less than 0,8
LnWO3N with Ln=Nd, Sm, Gd, Dy
Ln2.67W1.33O3.8N2.8, Ln14W4O33xe2x88x923xN2x, and Ln6W4O12xe2x88x923xN2x with 0 less than x with Ln=Ho, La, Nd, Sm, Y, Yb, and other alike defect compounds having a structure of A4X6.6xcex941.4 and A4X7.33 to 6.85xcex940.67 to 1.15, in which A=cations such as rare earth and tungsten, X=oxygen and nitrogen as anions, and xcex94 is a defect.
Ln2AIO3N with Ln=La, Nd, Sm
Ln10Si6O24N2 with Ln=La, Ce, Nd, Sm, Gd and Y
Ln2Si3O3N4 with Ln=Laxe2x80x94Yb and Y
Zr(x)Ta(3xe2x88x92x)O(x)N(5xe2x88x92x) with 0xe2x89xa6xxe2x89xa60.66
Ta(1xe2x88x92x)Zr(x)N(1xe2x88x92x)O(1+x) with 0xe2x89xa6xxe2x89xa60.28
3) oxynitrides based on three metals
AZrxTa1xe2x88x92xO2+xN1xe2x88x92x with A=Ca, Sr, Ba, 0 less than x less than 1
LiNaPON, Re6WV2+xO12xe2x88x923xN2x with 0 less than x
Ln8Cr2Si6O24N2 with Ln=Laxe2x80x94Dy (i.e., an element between La and Dy, inclusive, in the Periodic Table)
Ln8MIV2Si6N4O22 with Ln=Laxe2x80x94Dy and MIV=Ti or Ge
LnEuIISiO3N with Ln=La, Nd, Sm
Ln4Si2N2O7 with Ln=Ndxe2x80x94Yb (i.e., an element between Nd and Yb, inclusive, in the Periodic Table) and Y
Pyrochlore structure: AxAxe2x80x22xe2x88x92xB2O5+xN2xe2x88x92x or Axe2x80x22B2xe2x88x92yBxe2x80x2yO5+yN2xe2x88x92y 
A=Mg2+, Ca2+, Sr2+, Ba2+, Zn2+
Axe2x80x2=Ln3+ (=rare earth), Bi3+, Al3+, Fe3+
B=V5+, Nb5+, Ta5+, Mo5+, W5+
Bxe2x80x2=Zr4+, Hf4+, Sn4+, Ge4+, Si4+, Nb4+, Ta4+
0xe2x89xa6x, y less than 2, with the exception Ln2TaO5N2 
Spinel structure: CD2xe2x88x92mDxe2x80x2mO4xe2x88x92mNm or C1xe2x88x92nCxe2x80x2nD2O4xe2x88x92nNn 
C=Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+
D=Al3+, Ga3+, In3+, Ti3+, V3+, Cr3+, Fe3+, Co3+, Ni3+
Dxe2x80x2=Zr4+, Hf4+, Sn4+, Ge4+, Si4+, Nb4+, Ta4+
Cxe2x80x2=AI3+, Ga3+, In3+, Ti3+, V3+, Cr3+, Fe3+, Co3+, Ni3+
0 less than m less than 2, 0 less than nxe2x89xa61
Elpasolite structure: Axe2x80x22QBO5xe2x88x92z, N1+z 
z=0 Q=C (bivalent metallic ion) Axe2x80x22CBO5N
z=1 Q=Axe2x80x3 (trivalent metallic ion) Axe2x80x22Axe2x80x2""BO4N2 
z=2 Q=Dxe2x80x3 (tetravalent metallic ion)
Axe2x80x22Dxe2x80x3BO3N3 
Axe2x80x2, B, C and D are defined above and
Axe2x80x3 represents Ln3+ (=rare earth) or Bi3+
Dxe2x80x2xe2x80x2 denotes a tetravalent metal ion
Perovskite structure: A1xe2x88x92uAxe2x80x2uBO2xe2x88x92uN1+u or Axe2x80x2B1xe2x88x92wBxe2x80x2wO1+wN2xe2x88x92w 
A=Mg2+, Ca2+, Si2+, Ba2+
Axe2x80x2=Ln3+ (=rare earth), Bi3+, Al3+, Fe3+
B=V5+, Nb5+, Ta5+
Bxe2x80x2=Zr4+, Hf4+, Sn4+, Ge4+
0xe2x89xa6u less than 1; 0 less than wxe2x89xa61, with the exception Ln2TaON2 
The thickness of the nitride respectively oxynitride layers can vary, for example, between 5 and 500 nm, yielding slight shades and flat angle color effect at low thicknesses and very pronounced hiding at high thicknesses. For the optimal interference effect, the preferred thicknesses are 50-350 nm, especially preferred 80-200 nm.
Preferred pearlescent pigments of the present invention are given in the following:
substrate+TaxOyNz, preferably TaON (x=y=z=1)
substrate+ZrxOyNz, preferably Zr2ON2 or Zr7O8N4 
substrate+V doped ZrxOyNz, preferably V-doped Zr2ON2 or Zr7O8N4w 
substrate+LaTaON2 
substrate+Pr doped ZrxOyNz, preferably Pr-doped Zr2ON2 or Zr7O8N4 
substrate+CaTaO2N
substrate+SrTaO2N
substrate+Zr2ON2 
substrate+Zr7O8N4 
substrate+Ta3N5 
substrate+TaON
substrate+ZrV2O4N2 
substrate+ZrPr6O10N2 
substrate+TiON+Ta3N5 
substrate+Ta3N5+TiO2 
substrate+TiO2+SiO2+Ta3N5 
substrate+Zr2ON2+TiO2 
substrate+TiON+Zr2ON2 
substrate+TiO2+Zr2ON2 
Especially preferred pigments are given in the following:
Mica+TaxOyNz 
Mica+ZrxOyNz 
Mica+V doped ZrxOyNz 
Mica+LaTaON2 
Mica+Pr doped ZrxOyNz 
Mica+CaTaO2N
Mica+SrTaO2N
Mica+Zr2ON2 
Mica+Zr7O8N4 
Mica+Ta3N5 
Mica+TaON
Mica+ZrV2O4N2 
Mica+ZrPrO10N2 
Mica+TiON+Ta3N5 
Mica+Ta3N5+TiO2 
Mica+TiO2+SiO2+Ta3N5 
Mica+Zr2ON2+TiO2 
Mica+TiON+Zr2ON2 
Mica+TiO2+Zr2ON2 
SiO2 flakes+TaxOyNz 
SiO2 flakes+ZrxOyNz 
SiO2 flakes+V doped ZrxOyNz 
SiO2 flakes+LaTaONz 
SiO2 flakes+Pr doped ZrxOyNz 
SiO2 flakes+CaTaO2N
SiO2 flakes+SrTaO2N
SiO2 flakes+Zr2ON2 
SiO2 flakes+Zr7O8N4 
SiO2 flakes+Ta3N5 
SiO2 flakes+TaON
SiO2 flakes+ZrV2O4N2 
SiO2 flakes+ZrPr6O10N2 
SiO2 flakes+TiON+Ta3N5 
SiO2 flakes+Ta3N5+TiO2 
SiO2 flakes+TiO2+SiO2+Ta3N5 
SiO2 flakes+Zr2ON2+TiO2 
SiO2 flakes+TiON+Zr2ON2 
SiO2 flakes+TiO2+Zr2ON2 
Al2O3 flakes+TaxOyNz 
Al2O3 flakes+ZrxOyNz 
Al2O3 flakes+V doped ZrxOyNz 
Al2O3 flakes+LaTaONz 
Al2O3 flakes+Pr doped ZrxOyNz 
Al2O3 flakes+CaTaO2N
Al2O3 flakes+SrTaO2N
Al2O3 flakes+Zr2ON2 
Al2O3 flakes+Zr7O8N4 
Al2O3 flakes+Ta3N5 
Al2O3 flakes+TaON
Al2O3 flakes+ZrV2O4N2 
Al2O3 flakes+ZrPr6O10N2 
Al2O3 flakes+TiON+Ta3N5 
Al2O3 flakes+Ta3N5+TiO2 
Al2O3 flakes+TiO2+SiO2+Ta3N5 
Al2O3 flakes+Zr2ON2+TiO2 
Al2O3 flakes+TiON+Zr2ON2 
Al2O3 flakes+TiO2+Zr2ON2 
TiO2 flakes+TaxOyNz 
TiO2 flakes+ZrxOyNz 
TiO2 flakes+V doped ZrxOyNz 
TiO2 flakes+LaTaONz 
TiO2 flakes+Pr doped ZrxOyNz 
TiO2 flakes+CaTaO2N
TiO2 flakes+SrTaO2N
TiO2 flakes+Zr2ON2 
TiO2 flakes+Zr7O8N4 
TiO2 flakes+Ta3N5 
TiO2 flakes+TaON
TiO2 flakes+ZrV2O4N2 
TiO2 flakes+ZrPr6O10N2 
TiO2 flakes+TiON+Ta3N5 
TiO2 flakes+Ta3N5+TiO2 
TiO2 flakes+TiO2+SiO2+Ta3N5 
TiO2 flakes+Zr2ON2+TiO2 
TiO2 flakes+TiON+Zr2ON2 
TiO2 flakes+TiO2+Zr2ON2 
Fe2O3 flakes+TaxOyNz 
Fe2O3 flakes+ZrxOyNz 
Fe2O3 flakes+V doped ZrxOyNz 
Fe2O3 flakes+LaTaONz 
Fe2O3 flakes+Pr doped ZrxOyNz 
Fe2O3 flakes+CaTaO2N
Fe2O3 flakes+SrTaO2N
Fe2O3 flakes+Zr2ON2 
Fe2O3 flakes+Zr7O8N4 
Fe2O3 flakes+Ta3N5 
Fe2O3 flakes+TaON
Fe2O3 flakes+ZrV2O4N2 
Fe2O3 flakes+ZrPr6O10N2 
Fe2O3 flakes+TiON+Ta3N5 
Fe2O3 flakes+Ta3N5+TiO2 
Fe2O3 flakes+TiO2+SiO2+Ta3N5 
Fe2O3 flakes+Zr2ON2+TiO2 
Fe2O3 flakes+TiON+Zr2ON2 
Fe2O3 flakes+TiO2+Zr2ON2 
BiOCl+TaxOyNz 
BiOCl+ZrxOyNz 
BiOCl+V doped ZrxOyNz 
BiOCl+LaTaONz 
BiOCl+Pr doped ZrxOyNz 
BiOCl+CaTaO2N
BiOCl+SrTaO2N
BiOCl+Zr2ON2 
BiOCl+Zr7O8N4 
BiOCl+Ta3N5 
BiOCl+TaON
BiOCl+ZrV2O4N2 
BiOCl+ZrPr6O10N2 
BiOCl+TiON+Ta3N5 
BiOCl+Ta3N5+TiO2 
BiOCl+TiO2+SiO2+Ta3N5 
BiOCl+Zr2ON2+TiO2 
BiOCl+TiON+Zr2ON2 
BiOCl+TiO2+Zr2ON2 
Mica+TiO2+TaxOyNz 
Mica+TiO2+ZrxOyNz 
Mica+TiO2+V doped ZrxOyNz 
Mica+TiO2+LaTaONz 
Mica+TiO2+Pr doped ZrxOyNz 
Mica+TiO2+CaTaO2N
Mica+TiO2+SrTaO2N
Mica+TiO2+Zr2ON2 
Mica+TiO2+Zr7O8N4 
Mica+TiO2+Ta3N5 
Mica+TiO2+TaON
Mica+TiO2+ZrV2O4N2 
Mica+TiO2+ZrPr6O10N2 
Mica+TiO2+TiON+Ta3N5 
Mica+TiO2+Ta3N5+TiO2 
Mica+TiO2+TiO2+SiO2+Ta3N5 
Mica+TiO2+Zr2ON2+SiO2+TiO2 
Mica+TiO2+TiON+Zr2ON2 
Mica+TiO2+TiO2+Zr2ON2 
Mica+TiO2+SiO2+TiO2+TaxOyNz 
Mica+TiO2+SiO2+SiO2+TiO2+ZrxOyNz 
Mica+TiO2+SiO2+TiO2+V doped ZrxOyNz 
Mica+TiO2+SiO2+TiO2+LaTaON2 
Mica+TiO2+SiO2+TiO2+Pr doped ZrxOyNz 
Mica+TiO2+SiO2+TiO2+CaTaO2N
Mica+TiO2+SiO2+TiO2+SrTaO2N
Mica+TiO2+SiO2+TiO2+Zr2ON2 
Mica+TiO2+SiO2+TiO2+Zr7O8N4 
Mica+TiO2+SiO2+TiO2+Ta3N5 
Mica+TiO2+SiO2+TiO2+TaON
Mica+TiO2+SiO2+TiO2+ZrV2O4N2 
Mica+TiO2+SiO2+TiO2+ZrPr6O10N2 
Mica+TiO2+SiO2+TiO2+TiON+Ta3N5 
Mica+TiO2+SiO2+TiO2+Ta3N5+TiO2 
Mica+TiO2+SiO2+TiO2+TiO2+SiO2+Ta3N5 
Mica+TiO2+SiO2+TiO2+Zr2ON2+TiO2 
Mica+TiO2+SiO2+TiO2+TiON+Zr2ON2 
Mica+TiO2+SiO2+TiO2+TiO2+Zr2ON2 
The interference color is determined by the optical thickness, which is the geometrical thickness of the layer multiplied by the refractive index (Pfaff, G.; Reynders, P. xe2x80x9cAngle-dependent optical effects deriving from submicron structures of films and pigmentsxe2x80x9d, Chemical Reviews, 99 (1999), p. 1963-1981). The latter is a strong function of the chosen nitride respectively oxynitride but is in general not known for the rather new materials mentioned in this invention. The mass tone of the absorbing pigments is as well a function of the layer thickness. Therefore, the desired color effect is empirically optimized by adjustment of the amount of precursor, leading to a precursor layer thickness, and consequent reaction with the reactive gases.
The nitride respectively oxynitride layer can be coated directly onto the substrate, platelet-shaped, spherical or acicular substrates, as described above. Nitride respectively oxynitride layer coated particles can be used as substrates to precipitate the low refractive or high refractive optical layers, such as silicon dioxide, aluminum oxide, titanium oxides, iron oxides, ilmenite or pseudobrookite. The deposition of thin semi-transparent metal layers, such as chromium, silver, copper and aluminum, onto the nitride respectively oxynitride layers is also possible.
The mean diameter of the substrates and hence the resulting pigments can vary between 1 and 500 xcexcm, preferably between 5 and 50 xcexcm. For the flaky substrates and pronounced interference effects the preferred mean diameter is chosen between 5 and 150 xcexcm. Such substrates are commercially available or can be obtained by known processes.
The advantage of this invention is the combination of a great variety of different mass-tones of various nitrides and oxynitrides with an angle dependent interference color that is adjusted by the layer thickness of the nitride, respectively oxynitride layer.
To enhance the light and weather stability it is frequently advisable depending on the field of application, to subject the inventive pearlescent pigments to a surface treatment. Useful surface treatments and aftertreatments include for example the processes described in DE C 22 15 191, DE-A 31 51 354, DE-A 32 35 017 or DE-A 33 34 598, DE 40 30 727 A1, EP 0 649 886 A2, WO 97/29059, WO 99/57204, U.S. Pat. No. 5,729,255. This surface treatment further enhances the chemical stability of the pigments and/or facilitates the handling of the pigments, especially its incorporation into various application media.
The pearlescent pigments of the present invention are advantageously useful for many purposes, such as the coloring of plastics, glasses, ceramic products, agricultural foils, decorative cosmetic formulations, and in particular coatings, powder coatings, especially automotive coatings, and inks, including printing inks. All customary printing processes can be employed, for example offset printing, intaglio printing, bronzing, flexographic printing. Additionally the inventive pigments are suitable for the lasermarking of papers and plastics, for security applications like for example banknotes, ID cards, credit cards, concert tickets and plastic films.
The pearlescent pigments of the present invention are also advantageously useful for these purposes in admixture with filler pigments or transparent and hiding white, colored and black organic and inorganic pigments and also with conventional transparent, colored and black luster pigments based on metal oxide coated mica, TiO2 flakes, SiO2 flakes or Al2O3 flakes and coated or uncoated metal pigments, BiOCl pigments, platelet shaped iron oxides, or graphite flakes. The inventive pigments can be further coated with organic or inorganic layers to yield combination pigments.
The examples which follow are intended to illustrate the invention without, however, limiting it.
The entire disclosures of all applications, patents and publications, cited herein and of corresponding European application No. 02002448.5, filed Feb. 1, 2002, are incorporated by reference herein.